The present invention relates to a diagnosis system for a motor vehicle, and more particularly to a system provided with a device for checking automotive electric systems.
Recently, a motor vehicle has been equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption, and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if malfunctions of components and sensors occur, the engine does not properly operate.
However, because of the complexity of the electronic control system, it is difficult to immediately find out trouble. Accordingly, a trouble diagnosis device for easily checking the electronic control system should be provided as equipment in an auto shop.
Japanese Patent Application Laid-Open No. 58-12848 discloses a diagnosis system in which an exclusive checking device is provided for measuring a pulse duration of fuel injection and an engine speed, and for checking whether idling speed is normal. The checking device is provided for diagnosing only designated specific types of motor vehicles.
However, the main aim of the conventional diagnosis system is to monitor input and output signals of the electronic control system. Accordingly, at trouble shooting, in order to check voltage of elements such as various switches and electronic meters in an automotive electric system, or to check the grounding or connection of harness thereto in an electric circuit, a tester must be additionally used. Thus, the operation becomes troublesome.